Offset compound gear inline two-speed drive

ABSTRACT

A two-speed transmission having an input shaft and an output shaft, the transmission being capable of transitioning between fixed ratios, the high-range ratio being direct 1:1 and the low-range ratio being about 2:1. The transmission is a simple lightweight, yet robust, configuration utilizing only two gear meshes, being comprised of an input gear, a cluster gear, and an output gear. The transmission is controlled with a clutch and a sprag and with the input and output shafts turning in the same direction.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention described herein was made by an employee of the UnitedStates Government and may be manufactured and used by or for theGovernment for Government purposes without the payment of any royaltiesthereon or therefore.

TECHNICAL FIELD

The invention relates to transmissions, and more particularly to adevice(s) and configurations which provide a simple, lightweighttwo-speed drive which can be used either as an overall transmission oras a supplemental add-on input transmission (e.g.,over-drive/under-drive) to extend the capability of an existingtransmission.

BACKGROUND

In several recent studies and on-going developments for advancedrotorcraft, the need for variable or multi-speed capable rotors has beenraised. A speed change of up to 50% has been proposed for futurerotorcraft to improve overall vehicle performance. Accomplishing rotorspeed changes during operation requires both a rotor that can performeffectively over the operational speed-load range, and a propulsionsystem that can enable these speed changes.

Rotorcraft propulsion is a critical element of the overall rotorcraft.Unlike fixed wing aircraft, the rotor propulsion system provides liftand control as well as forward thrust. As a result, the rotorcraftengine-gearbox system must be highly reliable and efficient. Inaddition, the gearbox system must be kept at minimum weight. Presently,the propulsion system accounts for up to 25% of empty vehicle weight.The drive system accounts for up to 72% of the total propulsion systemweight. Future rotorcraft trends call for more versatile, efficient, andpowerful aircraft, all of which challenge state-of-the-art propulsionsystem technologies. Variable speed rotors have been identified ashaving a large impact on many critical rotorcraft issues.

Currently, rotor speed can only be varied a small percentage byadjusting the speed of the engine. The variation in rotor speed isgenerally limited by engine efficiency and stall margin, permittingspeed changes limited to approximately 15% when used in currenttilt-rotor applications.

There is a need for a transmission with a high-range ratio (1:1) forhover mode operation and low-range reduction ratio, such as for example50% (2:1), through a speed change mechanism, for cruise mode operation.A transmission of this type could be incorporated as an element withinthe overall propulsion system resulting in overall ratios of 50:1 to100:1 in the aircraft.

It is commonly recognized that variable speed propulsion is required forthe design of future advanced rotorcraft. Reductions in rotor speed arerequired to limit the advancing rotor tip speed and reduce rotor noise.

RELATED PATENTS

The following patents are incorporated by reference in their entiretyherein.

U.S. Pat. No. 7,044,877 to Ai discloses for example a two speedtransmission having an input shaft and an output shaft. The two-speedtransmission is capable of changing the rotating speed of the outputshaft from a first speed ratio to a second speed ratio. The shiftbetween the first rotating speed ratio and the second rotating speedratio is smoothly accomplished by the combination of two sets ofplanetary gear clusters and two electric motors. The electric motorsbeing are to smooth the mechanical shift between the first speed ratioand the second speed ratio. However, Ai does not disclose a transmissionwith a high-range ratio (1:1) and low-range reduction ratio, such as forexample 50% (2:1), which changes from one to the other through a speedchange mechanism including gears, a clutch and a sprag.

U.S. Pat. No. 6,641,365 to Karem disclosed for example “A variable speedhelicopter tilt rotor system and method for operating such a system areprovided which allow the helicopter rotor to be operated at an optimalangular velocity in revolutions per minute (RPM) minimizing the powerrequired to turn the rotor thereby resulting in helicopter performanceefficiency improvements, reduction in noise, and improvements in rotor,helicopter transmission and engine life.”

US Patent Application No. 2007/0205321 to Waide discloses for examplegearboxes providing first and second power-balanced paths in which aspeed changer is configured to operate with only one path. Mostpreferably, the gearbox includes a friction clutch and a sprag clutcharranged such that, together with a lay-shaft and spur-geardifferential, gear shifting can be done while transmitting power. Thespeed changing gearbox of the '321 application has first and secondindependently and concurrently operational drive paths for transmissionof torque. However, Waide does not disclose a transmission with ahigh-range ratio (1:1) and low-range reduction ratio, such as forexample 50% (2:1), which changes from one to the other and directs thetorque through an output shaft which is in the same drive path as theinput shaft.

SUMMARY OF THE INVENTION

With the present invention, a transmission, preferably for a rotorcraftis provided where the rotation of the rotor blades can be at 50% or lesswhile maintaining engine speed at the optimal efficiency/performancespeed. A portion of the overall 50% reduction can come from extendingthe engine speed operability range beyond present 15% decrease with thebalance provided by the transmission of the present invention. At thepresent time, the reduction in rotor speed of about 15% is presentlyaccomplished by changing the engine speed. However, with thetransmission of the present invention, the entire 50% decrease inrotational speed can be realized without requiring any additionalreduction in the speed of the engine. Future overall propulsion system(engine, driveline, and rotor) studies will determine what portion thetransmission device should provide for overall optimal performance. Thisinvention uniquely provides both a high-speed 1:1 range and a low-speed2:1 range (50% speed reduction) with minimal robust parts. The low rangeratio being dependent upon the gearing contained within can be varied,as required, to meet specific requirements.

According to the present invention, there is disclosed a transmissionhaving a gear arrangement for transmitting torque from an input shaft toan output shaft. The input shaft rotates about a first rotational axisand has a first gear coupled thereto. An elongated, hollow, cylindricalshaft rotates about a second rotational axis that is offset from thefirst rotational axis. The hollow cylindrical shaft has a second gear atone end there of which meshes with the first gear and a third ring gearat an opposite end thereof. A fourth gear is mounted to one end of ahollow drive shaft. The fourth gear and the hollow drive shaft rotateabout the first rotational axis. The fourth gear is meshed with thethird gear of the hollow, cylindrical shaft. The hollow drive shaft hasa cylindrical end portion at an opposite end thereof. The output shaftrotates about the first rotational axis and has a flange portionattached thereto. A sprag clutch has an input side mounted to thecylindrical end portion of the hollow drive shaft and an output sidemounted to the flange portion of the output shaft. A multi-plate clutchis attached to an end portion of input shaft and to the output shaft.Coupling structure is provided for coupling the input shaft with theoutput shaft whereby the transmission operates in first and secondmodes.

Further according to the present invention, the first mode of operationresults in a rotating speed ratio R₁ of 1 to 1 between the input shaftand the output shaft and the second mode of operation results in therotating speed reduction ratio range of 4.00>R₂>1.50 between the inputshaft and the output shaft. Preferably, the second mode of operationresults in the rotating speed reduction ratio range of 2 to 1 betweenthe input shaft and the output shaft.

Still further according to the present invention, coupling structure forcoupling the input shaft with the output shaft can cause the rotationalspeed of the output shaft to be the same as the rotational speed of theinput shaft is the multi-plate clutch.

Yet further according to the present invention, the clutch is amulti-plate clutch having first spaced clutch plates driven by an endportion of the input shaft and second spaced clutch plates which drivethe output shaft and interspersed between the first spaced clutchplates.

Moreover, according to the present invention, a clutch actuator meansengages or disengages the first and second interspersed clutch plateswhereby if the multi-plate clutch is engaged the rotational speed of theoutput shaft is at a first speed which is the same as that of the inputshaft and if the clutch is disengaged the rotational speed of the outputshaft is at a speed that is different from that of the input shaft.

Also, according to the present invention, the multi-plate clutch causesthe rotational speed of the output shaft to be the same as therotational speed of the input shaft whereby the transmission operates infirst mode (high speed range, 1:1 ratio).

Also, according to the present invention, the sprag clutch causes therotational speed of the output shaft to be less than the rotationalspeed of the input shaft whereby the transmission operates in secondmode (low speed range, 2:1 ratio).

According to the present invention, the first gear has external teethadapted to mesh with the internal teeth of the second gear and thirdgear has external teeth adapted to mesh with the internal teeth offourth gear.

Further according to the present invention, the relationship between theoutput rotational speed and the input rotational speed for the secondmode of operation is given by the equation

${{Output}\mspace{14mu}{speed}} = {{Input}\mspace{14mu}{speed} \times \left( \frac{N_{14}}{N_{30}} \right) \times \left( \frac{N_{34}}{N_{18}} \right)}$where N₁₄ is equal to the number of teeth on first gear, N₃₀ is equal tothe number of teeth on the second gear, N₃₄ is equal to the number ofteeth on the third gear, and N₁₈ is equal to the number of teeth on thefourth gear.

Still further according to the present invention, the input shaft isdriven by a device from which it receives rotational power such as anengine or an intermediate drive coupling if the present invention isadded to an existing design engine-transmission driveline and used as asupplemental inline speed change device.

Yet further according to the present invention, the first input shaft ofthe transmission is connected to the output shaft of a second geararrangement for transmitting torque from a second input shaft to thefirst input shaft. The second gear arrangement comprises a second inputshaft rotating about the first rotational axis and having a first gearcoupled thereto. An elongated, hollow, cylindrical shaft rotating aboutthe second rotational axis is offset from the first rotational axis. Thehollow cylindrical shaft having a second gear at one end thereof whichengages the first gear and a third gear at an opposite end thereof. Afourth gear is supported by a bearing at the aft end of the input shaftof the transmission.

Still further according to the present invention, the relationshipbetween the output speed and input for low speed operation of the secondgear arrangement is given by the equation:Output Speed=Input Speed×(N ₄₁₄ /N ₄₃₀)×(N ₄₃₄ /N ₄₁₈)

-   -   where N₁₄ is equal to the number of teeth on first gear (414),    -   N₃₀ is equal to the number of teeth on the second gear (430),    -   N₃₄ is equal to the number on the third gear (434),    -   and N₁₈ is equal to the number of teeth on the fourth gear        (418).

Yet further according to the present invention, the transmission is arotorcraft transmission of a light weight configuration with reducedparts.

According to the present invention, there is disclosed a method oftransmitting torque from an input shaft to an output shaft of atransmission. The method includes the steps of rotating the input shafthaving a first gear coupled thereto about a first rotational axis;rotating an elongated, hollow, cylindrical shaft about a secondrotational axis that is offset from the first rotational axis, thehollow cylindrical shaft having a second gear at one end thereof whichengages the first gear and a third gear at an opposite end thereof;rotating a fourth gear mounted to one end of a hollow drive shaft with acylindrical end portion at an opposite end thereof about the firstrotational axis whereby the fourth gear engages the third gear of thehollow, cylindrical shaft; rotating the output shaft with a flangeportion attached thereto about the first rotational axis; mounting aninput side of a sprag clutch to the cylindrical end portion of thehollow drive shaft and an output side of the sprag clutch to the flangeportion of the output shaft; and coupling the input shaft with theoutput shaft whereby the transmission (10) operates in first or secondmodes.

Further according to the present invention, there is disclosed the stepsof operating in the first mode of operation resulting in a rotatingspeed ratio R₁ of 1 to 1 between the input shaft and the output shaft;and operating in the second mode of operation resulting in the rotatingspeed ratio R₂ of and the second mode of operation results in therotating speed reduction ratio range of 4.00>R₂>1.50 between the inputshaft and the output shaft.

Still further according to the present invention, means are provided forattaching first spaced clutch plates of a multi-plate clutch to an endportion of input shaft and attaching second spaced clutch plates to theoutput shaft whereby the second clutch plates are interspersed betweenthe first spaced clutch plates; and engaging the first and secondinterspersed clutch plates whereby the rotational speed of the outputshaft is the same as that of the input shaft or disengaging the firstand second interspersed clutch plates whereby the rotational speed ofthe output shaft is less than that of the input shaft.

Also according to the present invention, there is disclosed a method oftransferring torque from an input shaft to an output shaft of atransmission including the steps of operating in the first mode ofoperation resulting in a rotating speed ratio R₁ of 1 to 1 between theinput shaft and the output shaft; and operating in the second mode ofoperation resulting in the rotating speed ratio R₂ of 2 to 1 between theinput shaft and the output shaft.

Further according to the present invention, there is disclosed a methodof transferring torque from an input shaft to an output shaft of atransmission including the step of engaging or disengaging themulti-plate clutch whereby when the multi-plate clutch is engaged therotational speed of the output shaft is at a first speed which is thesame as that of the input shaft and when the multi-plate clutch isdisengaged the rotational speed of the output shaft is at a speed thatis less than that of the input shaft.

Also according to the present invention, there is disclosed the steps ofengaging or disengaging the clutch whereby when the clutch is engagedthe rotational speed of the output shaft is at a first speed which isthe same as that of the input shaft and when the clutch is disengagedthe rotational speed of the output shaft is at a speed that is less thanthat of the input shaft.

Still further according to the present invention, there is disclosed thesteps of coupling the input shaft with the output shaft to cause thetransmission to operate in the first mode with the rotational speed ofthe output shaft the same as the rotational speed of the input shaft iswith the multi-plate clutch.

Still further according to the present invention, there is disclosed thesteps of coupling the input shaft with the output shaft to cause thetransmission to operate in the second mode with the rotational speed ofthe output shaft less than the rotational speed of the input shaft iswith the sprag clutch where the output speed is governed by the overallratio of the gear set comprised of the first, second, third and fourthgears.

Yet further according to the present invention, there is disclosed thestep of connecting the input shaft to a device that transmits rotationalpower.

Further according to the present invention, there is disclosed the stepof serially connecting a plurality of gear arrangements and determiningthe overall output ratio of the two serially connected gear arrangementsfrom the product of the two in-series ratios, R₁, R₂.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made in detail to embodiments of the disclosure,examples of which may be illustrated in the accompanying drawing figures(FIGs). The figures are intended to be illustrative, not limiting.Although the invention is generally described in the context of theseembodiments, it should be understood that it is not intended to limitthe invention to these particular embodiments.

Certain elements in selected ones of the figures may be illustratednot-to-scale, for illustrative clarity. The cross-sectional views, ifany, presented herein may be in the form of “slices”, or “near-sighted”cross-sectional views, omitting certain background lines which wouldotherwise be visible in a true cross-sectional view, for illustrativeclarity. In some cases, hidden lines may be drawn as dashed lines (thisis conventional), but in other cases they may be drawn as solid lines.

If shading or cross-hatching is used, it is not intended to be of use indistinguishing one element from another (such as a cross-hatched elementfrom a neighboring un-shaded element). It should be understood that itis not intended to limit the disclosure due to shading or cross-hatchingin the drawing figures.

FIG. 1 is an oblique cross sectional view of a two-speed,mechanical-power-conveying transmission, according to the presentinvention.

FIG. 2A is an orthogonal cross sectional view of the two-speed,mechanical-power-conveying transmission, according to the presentinvention.

FIG. 2B is a schematic axial view of the gear relationships in thetwo-speed, mechanical-power-conveying transmission, in according to thepresent invention.

FIG. 3A is an orthogonal cross sectional view of the present inventionshowing the path of power flow during high-speed output operation of thetwo-speed, mechanical-power-conveying transmission, according to thepresent invention.

FIG. 3B is an orthogonal cross sectional view of the present inventionshowing the path of power flow during low-speed output operation of thetwo-speed, mechanical-power-conveying transmission, according to thepresent invention.

FIG. 4 is an orthogonal cross sectional view of multiple stages of thetwo-speed, mechanical-power-conveying transmission in series, accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the descriptions set forth herein, various features of theinvention may be described in the context of a single embodiment. Thefeatures, however, may also be provided separately or in any suitablecombination. Conversely, although the invention may be described hereinin the context of separate embodiments for clarity, the invention mayalso be implemented in a single embodiment. Furthermore, it should beunderstood that the invention can be carried out or practiced in variousways, and that the invention can be implemented in embodiments otherthan the exemplary ones described hereinbelow. The descriptions,examples, methods and materials presented in the description, as well asthe claims, should not be construed as limiting, but rather asillustrative.

If any dimensions are set forth herein, they should be construed in thecontext of providing some scale to the relationship between theelements. For example, a given element may have an equal, lesser orgreater dimension (such as diameter) than another element. Anydimensions that are important or critical will generally be identifiedas such. The term “at least” includes equal to or greater than. The term“up to” includes less than. Also, an open-ended range or ratio as “atleast 2:1” should be interpreted to include sub-ranges such as at least2:1, at least 5:1, and at least 10:1.

The present two-speed transmission invention 10 is referred to herein asa “transmission,” “two-speed transmission,” “compound geartransmission,” or variations thereof, or as the inventors' preferredusage: “offset compound gear drive,” or OCG.

Referring to FIG. 1 there is shown in cross sectional view the noveltwo-speed, mechanical-power-conveying transmission 10 comprising aninput shaft 12 having a first gear 14 attached thereto, an output shaft26, an elongated, hollow, cylindrical shaft 16 having a second gear 30possessing internal teeth at one end 16 a of the cylindrical shaft, anda third gear 34 possessing external teeth at the other end 16 b of thecylindrical hollow shaft, a fourth gear 18 integral with or attached towheel 65 and supported on bearing 62 maintaining concentricity with gear14 by means of the aft end of shaft 12, a multi-plate clutch 22, and asprag clutch 28. The input shaft (12) is rotationally driven by a device(13), such as an engine, from which it receives rotational power. Theelongated cylindrical shaft 16 has a rotational axis 19 that is offsetfrom a shared main rotational axis 21 of the input shaft 12 and theoutput shaft 26. Input shaft 12 is supported on bearings 60 and 62.Output shaft 26 is supported on bearings 64 and 66. Bearings 60 and 66serve as drive system main bearings. Bearings 62 and 64 serve asintermediate bearings. Bearing 62 maintains concentricity and permitsrelative differential rotational speeds between gear 18 and shaft 12.Bearing 64 serves as a pilot bearing between input shaft 12 and outputshaft 26 to maintain concentricity and permit relative differentialrotational motion between input shaft 12 and output shaft 26 (i.e.,differential rotational speeds). Bearings 60, 62, 64, and 66 share acommon central axis 21. Shaft 16 is supported on bearings 48 which areconcentric with the axis 19 and are offset from the central axis 21 ofbearings 60, 62, 64, and 66. The offset between the axis 19 and 21 is adirect function of the gear ratios. Bearings 60, 62, 64, and 66 arerepresented as rolling element type bearings but may also be of thefluid film type or magnetic type as warranted by overall transmissionspeed and power requirements, and bearings 48 which are represented asfluid film type journals may also be of the rolling element type.

The first gear 14 having external teeth, is affixed to the input shaft12, and meshes with the second gear 30 having internal teeth, on theforward end 16 a of the elongated hollow shaft 16. At the aft end 16 bof the elongated hollow shaft 16 is a third gear 34, having externalteeth, and which meshes with a fourth gear 18, having internal teeth.The fourth gear 18 is attached to a hollow drive shaft 20 at a forwardend 20 a, by means such as bolts 29 (see FIG. 2A). The opposite ordistal end 20 b of hollow drive shaft 20 has a cylindrical end portion20 c onto which is mounted the input side 28 a of a sprag clutch 28.

The output shaft 26 has an integral flange portion 43 that is locatedbetween opposite ends 26 a and 26 b of the output shaft 26. Flangeportion 43 has an upstanding rim 43 a with an inner surface 43 b thatreceives the output side 28 b of the sprag clutch 28. The input shaft 12has an end portion 12 b that is large in diameter as compared to theremainder of the input shaft 12.

A hollow cylinder 24, sized to accommodate the multi-plate clutchassembly 22, is attached or contiguous with the input shaft distal endportion 12 b of input shaft 12. The clutch assembly 22 has alternatingstacked clutch plates 22 a, 22 b, 22 c, 22 d (22 a-22 d) (see FIG. 2)that are driven by, and rotate at the same speed as hollow cylinder 24by means of spline or tooth engagement at the outer perimeter. Thespaced stacked plates 22 a-22 d engage by means of friction a set ofinterspersed stacked clutch plates 23 a, 23 b, 23 c, 23 d (23 a-23 d)which drive and rotate at the same speed as the output shaft 26 by meansof spline or tooth engagement at the inner perimeter. An annularlyarranged clutch actuator 51, which is mounted to and rotates with theend portion 12 b of input shaft 12, compresses or releases the clutch 22to cause it to engage or disengage during operation, as described hereinbelow. The configuration of the clutch actuator 51 is a mechanicalspring arrangement (e.g., helical coil, Belleville, diaphragm spring)activated and hydraulically released (e.g., by an annular piston). Amechanical fail safe feature is incorporated in the clutch release(disengagement) mechanism so that the clutch will be engaged if there isa failure of the clutch release mechanism. FIG. 2B provides an axialschematic view of the rotating components of the present transmissioninvention 10. The elements shown are the input shaft 12 (which has theoutput shaft 26 behind it and out of view), having the first gear 14attached thereto, a ball or roller type bearing 17, the second gear 30and the third gear 34 that are part of, and integral with, the offsethollow cylindrical shaft 16, and the fourth gear 18. The solid line 27defines the foreshortened, end view of the cylindrical surface plane ofbearings 48, which provide support to offset hollow shaft 16. The offsetaspect of the hollow driveshaft 16 is evident in the location of itsaxis of rotation 19 in relation to the axis of rotation 21 that isshared by the input shaft 12 and the output shaft 26. Axis of rotation21 is the central, or primary, machine axis on which the drive systeminput and output are centered, whereas axis of rotation 19 is asecondary axis of rotation on which some of the internal componentsbetween the input and output rotate, primarily hollow shaft 16, secondgear 30, and third gear 34. The dashed oval 37 a encompasses a firstmesh plane 37 where the first gear 14 meshes with the second gear 30,and the second dotted oval 41 a encompasses the second mesh plane 41where the third gear 34 meshes with the fourth gear 18. FIG. 2B in anidealized view combining mesh plane 37 and mesh plane 41 into a singleplane for presentation of the OCG Offset Compound Gear concept basis,whereas in the present invention the two mesh planes are separatedaxially.

A first bearing set 60 (see FIGS. 1 AND 2A) supports the input end 12 aof the input shaft 12. A first single bearing 62 supports the fourthgear 18 in relation to the input shaft 12. A second single bearing 64supports the output shaft 26 in relation to the input shaft 12. A secondbearing set 66 supports the output shaft 26. The hollow, cylindricaloffset shaft 16 is carried by bearings 48, which are of the fluid filmjournal/thrust type or rolling element bearing type based upon specifictransmission requirements.

Operational Dynamics

During operation, if the multi-plate clutch 22 is engaged, then therotational speed of the output shaft 26 is the same as that of the inputshaft 12 and the power flows directly from the input shaft 12 to theoutput shaft 26 through the multi-plate clutch 22 by means of torquetransmitted via friction created by the clamping force provided byreleasing clutch actuator 51. If the clutch 22 is disengaged, then therotational speed of the output shaft 26 is less than that of the inputshaft 12 and the power flows from the fourth gear 18 to the flangeportion 43 of the output shaft 26 by way of the sprag clutch 28. Theratio of the input rotational speed and the output rotational speed whenthe clutch 22 is disengaged is on the order of 2:1 as described or someother ratio as required.

The input/output speed ratio is a function of the effective respectivediameters of the first and second meshing gears 14 and 30, respectively,and the respective diameters of the third and fourth meshing gears 34and 18, respectively, as should be readily evident to those who areskilled in the art of transmission of rotary mechanical power. Theinput/output ratio is discussed in more detail hereinbelow.

The two-speed operation of the present transmission invention 10 becomesmore evident upon contemplation of cross sectional views of FIGS. 3A and3B. FIG. 3A illustrates high-speed operation of the present transmissioninvention 10, which takes place when the multi-plate clutch assembly 22is engaged. The direction of flow of rotary mechanical power is shown bymeans of the line 77 with arrowheads 77 a. The direction of flow ofmechanical rotary power is from input shaft 12, hollow cylinder 24, toclutch assembly 22 and through output shaft 26, such that the outputspeed is the same as the input speed (the output ratio is 1:1.)

FIG. 3B illustrates low-speed operation of the present transmissioninvention 10, which takes place when the multi-plate clutch assembly 22is disengaged. Power enters at the input shaft 12 and is transferred byway of the first gear 14 to the second gear 30, which is contiguous withthe hollow driveshaft 16. The hollow driveshaft 16 conveys rotary powerto the contiguous third gear 34, which transmits it to the fourth gear18, which conveys it onward to the hollow drive shaft 20 that isaffixed, such as by means of bolts 29, to a wheel portion 65 of thefourth gear 18. The hollow driveshaft 20 conveys power to the spragclutch 28, which transmits it onward to the flange portion 43 of theoutput shaft 26, such that the output speed is less than the inputspeed, such as for example the output ratio is 2:1.

Input/Output Speed Ratios

The cylindrical offset shaft 16 comprises second and third gears 30 and34, respectively, disposed respectively at opposing ends 16 a and 16 hof the offset hollow shaft assembly. The second gear 30 has internalgear teeth 30′ and the third gear 34 has external gear teeth 34′. Thesecond gear 30 of the cylindrical offset shaft 16 receives mechanicalrotary power from the first gear 14 at the first gear mesh 52 (FIG. 2A)and then conveys the rotary mechanical power by means of the third gear34 that meshes with the fourth gear 18 at the second gear mesh 54.

The internal gear teeth 30′ of second gear 30 of the cylindrical offsetshaft 16 receive rotary force from the external gear teeth 14′ of thefirst gear 14; the external teeth 34′ of the third gear 34 conveysrotary force to the internal gear teeth 18′ of the fourth gear 18 whichconveys rotary mechanical power to the hollow driveshaft 20.Input/output speed ratios are determined by the respective numbers ofgear teeth 30′, 34′, 14′, 18′ of the two meshing gear sets, first andsecond gears 14, 30, respectively and third and fourth gears 34, 18,respectively.

The respective gear teeth 30′, 34′, 14′, 18′ of first and second gears14, 30, respectively and third and fourth gears 34, 18, respectively,can be of the straight cut spur varieties or of the helically cut orother gear teeth types such as herringbone as deemed necessary forrequired power rating operational reliability and quiet operation.

Note that all rotating parts described hereinabove rotate in the samedirection. Reductions in rotary speed take place at two locations: (1)at the first gear mesh 52 between the first gear 14 and the second gear30 of the cylindrical offset, double-gear assembly 16 and, (2) at thesecond gear mesh 54 between the third gear 34 of the second gear 18.

The relationship between the output speed and input for the low speedoperation is given by

${{Output}\mspace{14mu}{speed}} = {{Input}\mspace{14mu}{speed} \times \left( \frac{N_{14}}{N_{30}} \right) \times \left( \frac{N_{34}}{N_{18}} \right)}$where N₁₄ is equal to the number of teeth on first gear 14, N₃₀ is equalto the number of teeth on second gear 30, N₃₄ is equal to the number ofteeth on third gear 34, and N₁₈ is equal to the number of teeth onfourth gear 18.

The remainder of this section is a discussion on the ratio rangepotential of the OCG. The term “R” means the same as “ratio.”

The ratio-range potential for the speed reduction between the input andthe output shafts 12 and 26 of the OCG transmission 10 in a single-stageconfiguration is 4.00>R>1.50 (speed reduction output) and, conversely,it is 0.25<R<0.75 for a back driven, or reverse (speed increasingoutput) configuration. Preferably, however, the speed reduction ratiofrom the input to the output is 2:1 or R=2.

OCGs in Series Arrangement

Referring now to FIG. 4, there is shown, in cross-sectional schematicview, two OCGs 310, 410 coupled in such a way that the output of a firstOCG 310 is directed into a second OCG 410 so as to provide a seriesarrangement 300 wherein the overall ratio of input/output speedreduction (or multiplication) can be greater than that of a single OCG.It is possible, as those skilled in the art would clearly appreciate,that an unlimited number of OCGs could be so serially arranged, thoughpractical considerations would necessarily place limits.

The series arrangement 300, portrayed in FIG. 4, includes the first OCG310 which is comprised of the gear portion only of the transmission 10described hereinabove. The first OCG 310 has an input shaft 312 andthree moving parts with gears such that the input shaft drives a fifthgear 314, a hollow driveshaft 316, and an eight gear 318, whichcorrespond respectively to the first gear 14, the hollow driveshaft 16and the fourth gear 18 in the above described OCG transmission 10. Theoperational dynamics of the OCG gear train 310 need not be describedagain, as it is the same as that given hereinabove in relation to thebasic OCG transmission 10.

First OCG 310, as shown in FIG. 4, has an output shaft formed of aflange 313 which is secured to the eighth gear 318 by means such asscrews 329. The output shaft 413 is shown as being contiguous with,and/or is one in the same as, the input shaft 412 of the second OCGportion 410. The other parts of the second OCG portion 410, and theiroperational dynamics, are as described hereinabove in reference to theOCG transmission 10. It should be noted that the method of bolting theoutput shaft 313 to eighth gear 318 is only one of many such couplingmethods that could be used to greater or lesser advantage in the seriescoupling of the present OCG series arrangement 300. Splined connectionscould be used, or other types of bolted couplings, including flexible oruniversal joints could also be used, as called for by competentengineering judgment.

The second OCG portion 410 consists of the input shaft 412, a fifth gear414 (compare first gear 14), a hollow driveshaft 416, an eight gear 418(compare fourth gear 14), a hollow driveshaft 420 housing a clutch 422,a sprag clutch 428, and an output shaft 426, each of which, with theexception of the input shaft having the flange 413 has correspondingparts as described hereinabove in reference to the OCG transmission 10.That is to say, the second OCG transmission portion 410 displayed inFIG. 4 is of the same physical and operational sort that is describedhereinabove as the transmission invention 10.

In operation, the overall series arrangement 300 provides an overallrotational speed reduction between the input shaft 312 and the outputshaft 426 that is the multiplicative product of the speed reductionratio of the first OCG portion 310 and the speed reduction ratio of thesecond OCG portion 410. Thus the input/output speed reduction ratioexceeds that of a single OCG transmission 10. Note also that said speedreduction property could, upon reverse driving, provide a speedmultiplication, as should be obvious to those who are skilled in theart.

In the embodiment shown in FIG. 4, ratios above 4.00 can be configuredusing multiple stages of the transmission 10 in series. As an example,the OCG ratio range potential for the OCG Drive 10 in a two-stageconfiguration can provide R=16.00 by employing two R=4.00 (as the singlestage limit) in series (i.e., 16=4×4). Ratios between 4 and 16 can becreated using a combination of twin ratios or dual ratios in series. Aseries arranged dual-ratio, two-stage configuration would employconfigurations with two different OCG ratios to provide the desiredoverall output ratio. The overall ratio is defined as the product of thetwo in-series ratios, R₁, R₂ (i.e., R_(out)=R₁×R₂). The subject oftwo-stage configurations does not imply the use of two duplicateconfigurations, each with a clutch and sprag. More properly, it meansthat the OCG gearing would be employed in a two-stage configurationwhile maintaining the single clutch and sprag.

For a speed reduction of the sort the OCG was designed for, the upperand lower ratio limits are restricted by the geometrically possibleinput gear size. Above R=4.00, the input gear becomes impracticallysmall because the bearing size and shaft become impossibly small. BelowR=1.50, the input gear becomes too large creating gear toothinterference with the internal teeth of the second mesh.

Although the invention has been shown and described with respect to acertain preferred embodiment or embodiments, certain equivalentalterations and modifications will occur to others skilled in the artupon the reading and understanding of this specification and the annexeddrawings. In particular regard to the various functions performed by theabove described components (assemblies, devices, etc.) the terms(including a reference to a “means”) used to describe such componentsare intended to correspond, unless otherwise indicated, to any componentwhich performs the specified function of the described component (i.e.,that is functionally equivalent), even though not structurallyequivalent to the disclosed structure which performs the function in theherein illustrated exemplary embodiments of the invention. In addition,while a particular feature of the invention may have been disclosed withrespect to only one of several embodiments, such feature may be combinedwith one or more features of the other embodiments as may be desired andadvantageous for any given or particular application.

1. A transmission having a gear arrangement for transmitting torque froman input shaft to an output shaft, the gear arrangement comprising: theinput shaft rotating about a first rotational axis and having a firstgear coupled thereto; an elongated, hollow, cylindrical shaft rotatingabout a second rotational axis that is offset from the first rotationalaxis, the hollow cylindrical shaft having a second gear at one endthereof which engages the first gear and a third gear at an opposite endthereof; a fourth gear mounted to one end of a hollow drive shaft, thefourth gear and the hollow drive shaft rotating about the firstrotational axis, the fourth gear being meshed with the third gear of thehollow, cylindrical shaft, the hollow drive shaft having a cylindricalend portion at an opposite end thereof; the output shaft rotating aboutthe first rotational axis and having a flange portion attached thereto;a sprag clutch having an input side mounted to the cylindrical endportion of the hollow drive shaft and an output side mounted to theflange portion of the output shaft; a clutch attached to an end portionof input shaft and to the output shaft; and means for coupling anduncoupling the input shaft with the output shaft whereby thetransmission operates in first or second modes.
 2. The gear arrangementas recited in claim 1, wherein the first mode of operation results in arotating speed ratio R₁ of 1 to 1 between the input shaft and the outputshaft and the second mode of operation results in the rotating speedreduction ratio range of 4.00>R₂>1.50 between the input shaft and theoutput shaft.
 3. The gear arrangement as recited in claim 2, wherein thesecond mode of operation results in the rotating speed reduction ratiorange of 2 to 1 between the input shaft and the output shaft.
 4. Thegear arrangement as recited in claim 2, wherein the means for couplingthe input shaft with the output shaft causes the rotational speed of theoutput shaft to be the same as the rotational speed of the input shaft(i.e. ratio 1:1) is the clutch.
 5. The gear arrangement as recited inclaim 4, wherein the clutch is a multi-plate clutch having first spacedclutch plates driven by an end portion of the input shaft and secondspaced clutch plates driving the output shaft and interspersed betweenthe first spaced clutch plates.
 6. The gear arrangement as recited inclaim 4, further including a clutch actuator means to engage ordisengage the first and second interspersed clutch plates whereby if themulti-plate clutch is engaged the rotational speed of the output shaftis at a first speed which is the same as that of the input shaft and ifthe clutch is disengaged the rotational speed of the output shaft is ata speed that is less than that of the input shaft.
 7. The geararrangement as recited in claim 5, wherein the means for coupling theinput shaft with the output shaft to cause the rotational speed of theoutput shaft to be the same as the rotational speed of the input shaftwhereby the transmission operates in first mode is the multi-plateclutch.
 8. The gear arrangement as recited in claim 5, wherein the meansfor coupling the input shaft with the output shaft to cause therotational speed of the output shaft to be less than the rotationalspeed of the input shaft whereby the transmission operates in secondmode is the sprag clutch.
 9. The gear arrangement as recited in claim 1,wherein the first gear has external teeth adapted to engage internalteeth of the second gear and third gear has external teeth adapted toengage internal teeth of fourth gear.
 10. The gear arrangement asrecited in claim 7, wherein the relationship between the outputrotational speed and the input rotational speed for the second mode ofoperation is given by the equation${{Output}\mspace{14mu}{speed}} = {{Input}\mspace{14mu}{speed} \times \left( \frac{N_{14}}{N_{30}} \right) \times \left( \frac{N_{34}}{N_{18}} \right)}$where N₁₄ is equal to the number of teeth on first gear, N₃₀ is equal tothe number of teeth on the second gear, N₃₄ is equal to the number ofteeth on the third gear, and N₁₈ is equal to the number of teeth on thefourth gear.
 11. The gear arrangement as recited in claim 1, wherein theinput shaft is driven by a device from which it receives rotationalpower.
 12. The gear arrangement as recited in claim 1, wherein the firstinput shaft of the transmission is serially connected to the outputshaft of a second gear arrangement for transmitting torque from a secondinput shaft to the first input shaft, the second gear arrangementcomprises: the second input shaft rotating about the first rotationalaxis and having a fifth gear coupled thereto; an elongated, hollow,cylindrical shaft rotating about the second rotational axis that isoffset from the first rotational axis, the hollow cylindrical shafthaving a sixth gear at one end thereof which engages the fifth gear anda seventh gear at an opposite end thereof; and an eighth gear mounted tothe input shaft of the transmission.
 13. The gear arrangement as recitedin claim 11, wherein the overall output ratio of two serially connectedgear arrangements is the product of the two in-series ratios, R₁, R₂.14. The gear arrangement as recited in claim 1, wherein the transmissionis a rotorcraft transmission of a light weight configuration withreduced parts.
 15. The method of transmitting torque from an input shaftto an output shaft, comprising: rotating the input shaft having a firstgear coupled thereto about a first rotational axis; rotating anelongated, hollow, cylindrical shaft about a second rotational axis thatis offset from the first rotational axis, the hollow cylindrical shafthaving a second gear at one end thereof which meshes with the first gearand a third gear at an opposite end thereof; rotating a fourth gearmounted to one end of a hollow drive shaft with a cylindrical endportion at an opposite end thereof about the first rotational axiswhereby the fourth gear meshes with the third gear of the hollow,cylindrical shaft; rotating the output shaft with a flange portionattached thereto about the first rotational axis; mounting an input sideof a sprag clutch to the cylindrical end portion of the hollow driveshaft and an output side of the sprag clutch to the flange portion ofthe output shaft; attaching a clutch to an end portion of input shaftand to the output shaft; and coupling the input shaft with the outputshaft whereby the transmission operates in either a first or a secondmode.
 16. The method as recited in claim 14, including the steps of:operating in the first mode of operation resulting in a rotating speedratio R₁ of 1 to 1 between the input shaft and the output shaft; andoperating in the second mode of operation resulting in the rotatingspeed ratio R₂ of and the second mode of operation results in therotating speed reduction ratio range of 4.00>R₂>1.50 between the inputshaft and the output shaft.
 17. The method as recited in claim 14,further including the step of engaging or disengaging the clutch wherebywhen the clutch is engaged the rotational speed of the output shaft isat a first speed which is the same as that of the input shaft and whenthe clutch is disengaged the rotational speed of the output shaft is ata speed that is different than that of the input shaft.
 18. The methodof claim 16, including the step of coupling the input shaft with theoutput shaft to cause the transmission to operates in the first modewith the rotational speed of the output shaft the same as the rotationalspeed of the input shaft is with the multi-plate clutch.
 19. The methodof claim 14, including the step of connecting the input shaft to adevice that transmits rotational power.
 20. The method of claim 14,including the step of serially connected a plurality of geararrangements with the output shaft of a second gear arrangementtransmitting torque from a second input shaft to the first input shaftof a first gear arrangement comprising the steps of: rotating the secondinput shaft having a fifth gear coupled thereto about the firstrotational axis; rotating an elongated, hollow, cylindrical shaft aboutthe second rotational axis that is offset from the first rotationalaxis, the hollow cylindrical shaft having a sixth gear at one endthereof which meshes with the fifth gear and a seventh gear at anopposite end thereof; and mounting an eighth gear to the input shaft ofthe first gear arrangement.
 21. The method of claim 19 including thestep of taking the product of the two in-series ratios, R₁, R₂ todetermine the overall output ratio of the two serially connected geararrangements.